In April, two foreign graduate students from China were gunned down while sitting in their car, which was parked in a neighborhood off campus.

On Wednesday night, an argument broke out between two men outside the Ronald Tutor Center, where a party hosted by a campus student organization was being held, officials said. Moments later, one of the men pulled out a gun and shot his intended target in the torso three or four times, they said.

That victim was critically injured and was undergoing surgery at a local hospital. Three bystanders were also wounded with non-life-threatening injuries, officials said.

Authorities said the two suspects were chased by campus security officers and were quickly taken into custody about a football field's length away from the crime scene.

Asst. Chief John Thomas of the USC Department of Public Safety said at a news briefing Thursday morning that the shooting was "totally an isolated incident."

"There is no pending danger" to the university, he said.

None of the people involved in the matter were USC students, faculty or staff, authorities said.

No information was immediately available about which group was hosting the Halloween party on campus.

In a statement issued on the university's website, USC's vice president for student affairs, Michael L. Jackson, said that campus policy requires that student parties be open only to guests with student IDs from USC or another university.

"This incident reminds us that we must look out for ourselves and be particularly vigilant about the personal safety of friends and guests at our social events," Jackson said in the statement.

It is unclear whether anyone was checking identifications at the event. The shooting took place outside the party, where about 100 people were gathered, officials said.

Students who witnessed the incident described a chaotic scene.

"You hear one shot and you're like, 'Wait, what was that?'" said Matthew Hamilton, a graduate student who witnessed the incident. "As soon as it registered, everyone just ran."